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Making Sturdy Stuff Out of Plastic Sheets, Part 1: Mail Bins

By Rain Noe - May 6, 2011

in Materials

Walk around a U.S. city and you'll occasionally see these bins sitting next to mailboxes. The U.S. Postal Service uses them to haul periodicals and what they call "flats"--letters and envelopes--and occasionally leaves them next to a mailbox to be used by the next postal worker. The bins are sturdy as hell, which is why some people steal them.

They're made by folding up corrugated plastic sheets. The plastic is stronger than corrugated cardboard, and unlike cardboard, can be left out in the rain. Some type of crimping tool is used to crush a circle into the folded sheets, and a series of these crimped divots is strong enough to hold the surfaces together. The overall shape is designed to be trapezoidal rather than having 90-degree walls so that the bins can be stacked.

Whomever designed the bins added a metal rod bent into a rectangle that runs the perimeter of the rim, adding structure. Other than that the ribs in the plastic do the work, making the containers rugged enough to handle the tender ministrations of our exceedingly careful postal workers, who would never do things like throw piles of stuff out of the back of their truck onto the sidewalk.

If you're keen to try making one yourself, you can purchase this plastic in sheets up to 4x8 at art supply stores like Blick or at a plastics center.

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Paul St. Onge

8 years ago

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"Some type of crimping tool is used to crush a circle into the folded sheets, and a series of these crimped divots is strong enough to hold the surfaces together." The process used is called Ultra Sonic welding. Also note, that the "Corroplast board pictured has square flutes. The board pictured on the totes shown has fluting in the shape of a sine wave. Only two companies in North America make this laminated/corrugated board. Neither are Corroplast who is a manufacture of extruded plastic sheet. All plastic board is not Corroplast any more than all facial tissue is "Kleenex."

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Lance

10 years ago

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I've considered projects several times using Coroplast (the corrugated plastic sheet in question), but I could never get past the price-point and panel sizes to actually do anything with it. Prices are all over the board on it as a material (I've found it in India Industrial Supply places for as low as $30 a sheet, and in American supply stores for as much as $400 a sheet, and the same material!).
That said, the common size for this material is 24x48, and only Industrial bulk suppliers sell the full 48x96 sized sheets, and you have to purchase bulk quantities from them normally to get it (like 250 palletized sheets) at $45 a sheet.

Coroplast is an amazing product for 'waterproof concept requirements', but until they drop the price on it, it sure looks like vacuum-bonded polyethylene on plywood is a LOT more economical than this.
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david

13 years ago

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@ru thanks for the tip about looking for "coroplast". In the UK it's called "Correx", about 15pounds per 4 by 8 sheet from sign makers apparently.
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ru

13 years ago

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We have dozens of these to move parts around in the warehouse, I have put 50 + pounds in them no problems.
You can get them at uline here: http://www.uline.com/BL_303/Space-Age-Totes?keywords=uline_plastic_bins
Also, the brand name of the material is Coroplast if you are searching out this material. I have been able to purchase it from a local sign maker for $20 a 4x8 sheet.
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emanster provolone

13 years ago

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Great little article. Any additional detail on the heat pressing for fastening would be appreciated.

I'm just gonna throw this out there, since I dont have the time to make it, but some clever student will.

They look like laundry hampers to me. Would love to see a replica made for home use, with the lattering on the side that says, 'UNITED STATES LAUNDRY SERVICE'

There you go! I want 10% royalties!
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